Windshield wiper blades may be molded from a wide variety of elastomers including natural and synthetic rubbers, such as natural or synthetic polyisoprene, butadiene, ethylene-propylene-diene rubber, neoprene or blends thereof. Most generally, however, windshield wipers are made of natural or synthetic polyisoprene. In order for a windshield wiper blade to operate properly, the frictional drag of the blade across the windshield must be low. It is apparent that, if the frictional drag between the rubber and the glass can be reduced, the wiper assembly will require less power to operate. Likewise, reducing the frictional drag of the blades improves the wiping action since, as the drag increases, there is a tendency toward chattering of the blade as it is pulled over the glass. This is most commonly a problem when the windshield is only marginally wet and results in a streaked windshield during the wiping cycle. Thus, the blade must have a low degree of frictional drag in order to move over the glass with less effort and wipe the windshield more uniformly without streaks. Blades made with some elastomers, e.g., neoprene, possess a coefficient of friction which may be low enough so that no treatment to reduce the surface friction of the blade is required. However, most blade materials will require some treatment in order to reduce their surface friction.
Windshield wiper blades, typically made of polyisoprene, are generally treated by halogenating the surface of the wiper blade with either chlorine or bromine. The reaction of the halogen with the elastomer, by means of the ethylenic unsaturation present on the backbone of the elastomer, hardens the surface of the wiper blade and thus reduces its friction. It is also possible to reduce the friction of the blades by surface treatment with an inorganic acid such as nitric acid or sulfuric acid. Still another way to reduce the friction of a wiper blade is to coat the blade with a surface layer of friction reducing material, e.g., molybdenum disulfide, as is taught in U.S. Pat. No. 3,080,596.
Another attempt to form windshield wiper blades with improved wipe characteristics is described in U.S. Pat. No. 4,103,385. In that patent, the process of forming wiper blades comprises first treating the blade to harden is surface and then coating the surface hardened blade to lower its coefficient of friction, as for example, by first treating the blade with chlorine, and thereafter applying at least one coating comprising materials selected from elastomeric and plastic materials having a particular Young's modulus. It is taught therein that, where halogenation is ineffective to increase surface hardness, as in the case of blades made of ethylene-propylenediene rubber (i.e., because it is an elastomer having a saturated backbone), a first coater would apply a hardened layer on the surface of the blade, and then a second coater would apply the coating comprising the elastomeric and plastic materials.
However, while such coatings applied to windshield wipers may be effective to lower the frictional drag of the blade, the coatings may be worn off with use. Additionally, commonly employed windshield wipers, made of elastomers with unsaturated backbones such as natural rubber, are subject to chemical changes caused by environmental attack of the blade by, e.g., ultraviolet light, heat, oxygen and ozone during use. These chemical changes in the elastomer, generally by means of reactions at the unsaturated sites, change its physical properties. Consequently, the blade may stick to the windshield, losing particles when torn loose, and begins to harden and take a set so that it does not conform well to the windshield curvature. This results in a marked deterioration of the wipe characteristics of the wiper blades, necessitating their replacement.